1. Field of the Invention
This invention relates to a wide-angle zoom lens.
2. Description of Related Art
A zoom lens which includes, in order from the object side, a front lens unit with positive refracting power and a rear lens unit with negative refracting power has been often used because the number of lens components is small and its arrangement is simple. Zoom lenses in which an angle of view can be as wide as 70xc2x0 or more at a wide-angle position are known and disclosed, for example, in U.S. Pat. No. 4,936,661 and Japanese Patent Preliminary Publication Nos. Hei 6-82696, Hei 8-240771, Hei 10-39212, and Hei 10-311947.
The optical system of such a zoom lens includes an aspherical lens in the rear lens unit with negative refracting power, but each lens component of the rear lens unit is large in diameter and thus it is extremely difficult to make the aspherical lens. In particular, since an aspherical lens made of glass requires an advanced technique for the fabrication of the lens, manufacturing cost becomes so high that the aspherical lens cannot be used for an inexpensive product. Furthermore, when an aspherical lens is molded out of resin, it is liable to affect imaging performance, depending on variations in thickness and surface profile due to temperature changes or a way of fixing the lens to a frame member.
Other examples can be cited from Japanese Patent Preliminary Publication Nos. Hei 2-284109, Hei 3-200913, Hei 3-213814, and Hei 7-234363. In each of these examples, a rear lens unit is constructed with three glass lenses, and its fabrication and assembly are favorably performed since an aspherical surface is not used, but the variable magnification ratio of a zoom lens is as low as 2.4 or less. Moreover, since the magnification of each negative lens in the rear lens unit is high at a telephoto position and the shift of a focus position caused by size variations of parts becomes remarkable, it is difficult to increase the focal length at the telephoto position.
It is, therefore, an object of the present invention to provide a wide-angle zoom lens which includes a front lens unit with positive refracting power and a rear lens unit with negative refracting power so that the rear lens unit has, in order from the object side, a positive lens component and at least one negative lens component, and which is wide in angle of view at a wide-angle position, high in variable magnification ratio, low in cost, and easy in assembly.
In order to achieve the above object, the wide-angle zoom lens according to the present invention includes, in order from the object side, a front lens unit with positive refracting power and a rear lens unit with negative refracting power so that spacing between the front lens unit and the rear lens unit is changed to thereby vary the magnification of the zoom lens. In this case, the rear lens unit has, in order from the object side, a first lens component with positive refracting power and a second lens component with negative refracting power so that an aspherical surface is not included in any lens component, and satisfies the following conditions:
2.5 less than fT/fW less than 5xe2x80x83xe2x80x83(1)
0.7 less than tan xcfx89w less than 1.5xe2x80x83xe2x80x83(2)
where fT is the focal length of the entire system of the wide-angle zoom lens at the telephoto position, fW is the focal length of the entire system of the wide-angle zoom lens at the wide-angle position, and xcfx89w is a half angle of view at the wide-angle position.
Further, the wide-angle zoom lens according to the present invention includes, in order from the object side, a front lens unit with positive refracting power and a rear lens unit with negative refracting power so that spacing between the front lens unit and the rear lens unit is changed to thereby vary the magnification of the zoom lens. In this case, the rear lens unit has, in order from the object side, a first lens component with positive refracting power, a second lens component with negative refracting power, and a third lens unit with negative refracting power so that an aspherical surface is not included in any lens component, and satisfies Condition (2) and the following conditions:
2.1 less than ft/fW less than 5xe2x80x83xe2x80x83(1-1)
0.3 less than R1/R2 less than 0.65xe2x80x83xe2x80x83(3)
where R1 is the radius of curvature of the most image-side surface of the first lens component and R2 is the radius of curvature of the most object-side surface of the second lens component.
Still further, according to the present invention, the wide-angle zoom lens satisfies the following condition:
|f1/f2| less than 0.7xe2x80x83xe2x80x83(4)
where f1 is the focal length of the first lens component and f2 is the focal length of the second lens component.
This and other objects as well as the features and advantages of the present invention will become apparent from the following detailed description of the preferred embodiments when taken in conjunction with the accompanying drawings.